1. Field of the Invention
The present invention relates to a flexible, restrained pipe joint employing locking segments having an elastomeric backing and a separate fluid seal gasket, which is particularly useful with large diameter ductile iron pipe.
2. Description of Related Art
Heretofore, numerous locking arrangements have been proposed for use in bell-and-spigot type joints to restrain axial movement of the spigot end of one pipe section relative to the bell end of another pipe section in which the spigot end is disposed. Two examples of ring-type locking structures are shown in prior U.S. Pat. No. 4,428,604, issued to Conner, and U.S. Pat. No. 4,685,708, issued to Conner and Walworth, both of which are assigned to the assignee of the present invention.
U.S. Pat. No. 4,805,932, to Imhof, discloses a pipe joint wherein the joint locking or restraining means is separate from the sealing ring, and the locking means comprises a gripping ring having a plurality of toothed gripping pieces embedded in and spaced around a circumference of a rubber ring. In addition, a collar is attached to the rubber ring which extends outwardly to the exterior of the bell end of the pipe section, the collar being used to hold the gripping ring in place, and to facilitate handling of the gripping ring. That patent recognizes and discusses certain limitations or drawbacks associated with joint configurations wherein the gripping ring and the sealing ring are formed as a single unit. For example, sudden axial pressure has the tendency to cause substantial withdrawal of the spigot from the socket, and can possibly permit complete withdrawal if the gripping teeth do not engage the spigot in a timely manner. The Imhof patent specifically refers to West German Patent No. 2,034,325, which has U.S. Pat. No. 3,724,880, issued to Seiler, as its equivalent U.S. patent. Imhof notes that the sealing and gripping rings in that patent leave a relatively large distance between the convex exterior surface of the gripping segments and the interior surface of the pipe socket. It is therein noted that the first time internal pressure is applied in the pipes, the gripping ring and sealing ring must move (with the spigot) a substantial axial distance before the gripping segments can be in a position to attempt to bite into the outer surface of the spigot to retain the spigot within the bell or socket.
A further potential limitation with respect to the single unit gripping/sealing ring not mentioned in that patent is that the degree of permissible deflection of the members joined may, in certain instances, be limited. The Imhof patent itself has the disadvantage that the connecting segment (numeral 24 in that patent), which is used to pull or urge the locking ring toward the open end of the bell, can be pinched between the bell and spigot when the joint is over-deflected, and can be torn by the pinching action. Once torn, the connecting segment loses its effectiveness in maintaining the locking ring in its desired position.
While prior joint designs for restrained joints may generally be regarded as being satisfactory in performance in many instances, the present invention provides improvements over those designs particularly in providing resiliently positive locking engagement of the locking members within the pipe bell, and in providing greatly increased contact area of the locking elements with the spigot end of the pipe around the circumference thereof, improving the restraining characteristics of the joint in general, including improving the potential for increased deflection angles, and improving the ability of the locking ring to prohibit dirt from entering into joint recesses, particularly during back fill.
Another important advantage of the present invention, when compared to the separate rubber-metal locking ring of the Imhof '932 patent, is that the relatively less complicated shape of the present invention can be more simply and economically mold-bonded by virtue of its geometry in a conventional, two-piece rubber-forming mold. The more complicated shape of the Imhof '932 structure requires more complicated molds consisting of more than two working parts and/or more cumbersome molding procedures, by virtue of its rubber/metal geometry.
It is a principal object of the present invention to provide a restrained joint for a bell-and-spigot type joint having a fluid sealing member or gasket and separate elastomer-backed locking segments which provide improved retention forces on the spigot within the bell, and which provide the ability to achieve increased amounts of deflection between the piping elements joined.
It is an additional object of the present invention to provide a locking member for a restrained joint which may be modified for use with pipe sections having various sized diameters.
It is another principal object of the present invention to provide a restrained joint for bell-and-spigot type piping elements having elastomer-backed locking segments and a separate fluid sealing member wherein the locking segments and backing member or members assist in serving as an effective dirt seal to significantly reduce the amount of dirt and other materials from gaining access to interior joint regions such as the region where the fluid sealing member is disposed.
It is another important object of the present invention to provide a locking means which is separate from the fluid seal means wherein the locking means is of a geometry enabling the use of a more simple and economical molding process for forming an elastomeric backing ring having locking segments bonded thereto.
It is a further important object of the present invention to provide the above-stated advantages in a push-on type restrained joint.